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This paper presents a control strategy based on fuzzy logic to inject efficiently the active power from a three-phase grid-connected photovoltaic (PV) system into the local grid with supporting regulation for the frequency of grid voltage. In which the control strategy consists of three main modules as follows. Firstly, a simulation module based on the mathematical model of a PV panel is utilized to predict the maximum total power from PV arrays; the second one is a frequency regulation module used to compute a proper reference value for the output active power; and the last is a coordinated main controller for power-electronic converters and battery charger to deliver active power to the grid exactly according to the reference value computed beforehand. Especially in the frequency regulation module, a unique fuzzy logic controller (FLC) is designed to help determine accurately the reference value of active power. Besides, a control method for state-of-charge (SOC) of battery bank is also introduced. Simulations show the suggested control strategy has good performances in supplying suitably the active power to grid with regulating the grid frequency in acceptable ranges, even when the solar radiation or AC-system load suddenly changes. Also, effectiveness in regulating grid frequency of the proposed control strategy is compared with the conventional strategy using full maximum power point tracking (MPPT) mode. 

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This paper discusses two techniques based on the feedback linearization (FBL) method to control the active and reactive output powers of three-phase grid-connected photovoltaic (PV) inverters. The first control scheme is an application of the direct FBL approach. The other is an appropriate combination of the FBL and fuzzy logic (FBL-FL), and is the main proposed method of this study. Wherein, a unique fuzzy logic controller (FLC) is designed to enhance effectiveness of the linear control method used in the direct FBL. In detail, its major objectives are to improve the transient response and reduce steady-state oscillations in the output powers. In this research, the illustrative PV inverter utilizes a three-level DC-AC converter, an R-L filter and a 250 V/10 kV wyewye transformer to inject the energy, obtained from PV array with a nominal power of 100 kW, into the 10 kV/60Hz three-phase grid. Numerical simulations in MATLAB and PSIM illustrate that the two FBL-based structures perform very well in independently regulating the active and reactive output powers to the reference values, even within the parametric uncertainties and the unbalanced grid voltage condition. Moreover, comparisons of simulation results, obtained from the traditional proportional-integral (PI) control and the two FBL-based structures, show advantages of the proposed FBL-FL hybrid technique in terms of fast response, small overshoot, acceptable steady-state fluctuation and high robustness.